System and method for utilizing a linear sensor

ABSTRACT

Systems and methods for utilizing linear optoelectronic sensors are provided. A plurality of linear sensors may be utilized to obtain velocity measurements of a web material at two points. The acceleration of the web material may be determined from the velocity measurements and a control signal issued to a servo to maintain proper tension along the web material.

RELATED APPLICATIONS

This patent application is related to the following United States patent applications:

Ser. No. 11/763,752, entitled METHOD AND SYSTEM FOR OPTOELECTRONIC DETECTION AND LOCATION OF OBJECTS, by William M. Silver, the contents of which are hereby incorporated by reference,

Ser. No. 11/763,785, entitled METHOD AND SYSTEM FOR OPTOELECTRONIC DETECTION AND LOCATION OF OBJECTS, by William M. Silver, the contents of which are hereby incorporated by reference, and

Ser. No. 12/100,100, entitled METHOD AND SYSTEM FOR DYNAMIC FEATURE DETECTION, by William M. Silver, the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention is directed to optoelectronic sensors and, more specifically to applications of optoelectronic linear sensors.

BACKGROUND OF THE INVENTION

In modern production line environments, for both discrete object manufacturing and web based material manufacturing, various control systems are typically implemented to ensure product quality and compliance with applicable regulations. These control systems typically require a number of measurements of the web material and/or other objects along the production line. Exemplary measurements include draw control measurement of a web material to ensure that the tension on the material at various points stays within a predetermined range to prevent tearing, enable splicing, distance travelled measurements to enable cut to length operations and/or the acquisition of various statistical data measurement to ensure that the products meet a minimum set of standards, etc. Furthermore, product detection, velocity and/or location measurements may need to occur to enable certain operations, for example, the printing of an expiration date on a product box. Typically, optoelectronic sensors and/or physical measurement devices have been utilized for performing these tasks. Noted disadvantages of such physical monitoring sensors is that should a new form of monitoring be required, a production line may need to be halted and dramatic reconfigurations occur to support the new physical monitoring systems. Furthermore, physical monitoring systems typically lack easy configuration and/or integration with other systems in a production line environment.

Certain web material production environments may need accurate measurements of tension of the web material. Typically, these measurements are obtained by monitoring encoders that are operatively interconnected with a motor and/or roller shafts used to transport the web material These encoders are typically utilized to measure velocity of the web material; however, as noted above, a noted disadvantage of such encoder based monitoring is that the encoders may not provide accurate measurements due to, e.g., web material slippage, variations in material thickness, etc. Furthermore, changes in the material may cause inaccuracies when using conventional measuring techniques. More generally, conventional techniques introduce inaccuracies due to their indirect measurement of the object and/or material, i.e., conventional techniques measure a an encoder or drive speed and not the speed of the object or web material itself. As such, the measurements may not be accurate, thereby resulting in incorrect draw control information which may result in damaged and/or wasted material.

Furthermore, certain web material production environments may need to perform cut to length operations, i.e., operations that occur at substantially regular intervals along the web material. Examples of cut to length operations include, e.g., perforating paper towels at regular intervals, cutting diaper materials at regular intervals, etc. Typically, an encoder based measuring system is utilized to measure the velocity of the web material, which is then integrated over time to determine a distance that the material has traversed before an actuator is activated to perform the desired operation. However, as noted above, physical monitoring systems have a number of noted disadvantages. A first noted disadvantage is that inaccuracies may be introduced due to physical slippage, etc. along a conveyor and/or servo motor resulting in measurements that may not be as precise as necessary. The diameter of the roller to which an encoder is coupled may introduce additional inaccuracies. Furthermore, inaccurate measurements may be compounded due to increases in slippage, etc. as a machine ages, thereby further reducing the preciseness of system's measurement capabilities. A further noted disadvantage is that physical monitoring systems typically require substantial configuration and installation to add to a production line as well as periodic (re-)calibrations. This complicates installation and substantially increases the total cost of ownership of such measurement systems due to the opportunity cost of having a production line idle during the lengthy installation and/or during annual maintenance or (re-)calibrations. Additionally, physical limitations may prevent encoders from being located in desired positions along the web material. These limitations may complicate installation and/or prevent a system from obtaining measurements at desired locations.

As will be appreciated by one skilled in the art, conventional servo measurement systems, e.g., shaft encoders, etc., have a number of noted disadvantages. Furthermore, conventional machine vision systems and optical sensors typically do not provide adequate solutions. Machine vision systems typically are expensive and require substantial configuration to operate. Additionally, many of these tasks are not well suited for conventional machine vision systems as conventional machine vision systems cannot operate at a speed to sense the motion of the web material with a sufficiently high degree of accuracy. Optical sensors have noted disadvantages including, e.g., poor accuracy, etc.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of the prior art by providing a system and method for utilizing linear sensors to perform a plurality of measurement functions. Illustratively, one dimensional optical linear sensors are oriented substantially parallel to a direction of movement of objects and/or a web material to obtain measurement information. The linear sensors are illustratively the linear sensors described in the above-incorporated United States patent applications; however, in alternative embodiments, any linear sensor capable of obtaining accurate velocity and/or length measurements at a suitably high rate of speed may be utilized. In an illustrative embodiment of the present invention, such linear sensors may be easily added to an existing production line without substantial reconfiguration of the production line, thereby reducing the installation cost.

In an illustrative embodiment, a plurality of linear sensors are arranged along a web material production line. Velocity measurements of the material are obtained at a first location and a second location along the web material. The acceleration between the two points is then determined by measuring the difference between the two velocity measurements. As force is proportional to acceleration, the force (tension) along the web material between the two points is determined. Control signals are then transmitted to appropriate servo motors to adjust the tension along the web material, i.e., to perform draw control operations. In this way, draw control can be maintained without requiring physical monitoring systems.

In a further illustrative embodiment of the present invention, a linear sensor measures the length of a web material that traverses a particular point along the production line. When a predefined length of the material has passed the point, a control unit, operatively interconnected with the linear sensor, activates a trigger signal that causes an actuator to perform an action on the material. Illustratively, such an action may comprise cutting the material, perforating the material, printing onto the material, etc.

In another illustrative embodiment, linear sensors collect statistical data relating to the web material as it moves along a production line. The linear sensors may be utilized for other functions, e.g., cut to length operations, etc, or may be only utilized for acquisition of statistical data. The linear sensors acquire various statistical data that may be utilized to calculate a quality score. The computed quality score may be compared to a minimum quality score to determine whether material meets appropriate quality control requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings in which like reference numerals indicate identical or functionally similar elements:

FIG. 1 shows an example application of a system for detecting and locating discrete objects moving down a production line in accordance with an illustrative embodiment of the present invention;

FIG. 2 shows an example application of a system for tracking a moving continuous web in accordance with an illustrative embodiment of the present invention;

FIG. 3 shows a block diagram of an illustrative apparatus in accordance with an illustrative embodiment of the present invention;

FIG. 4 shows a portion of a capture process that obtains an image of a field of view, where the image is oriented approximately parallel to a direction of motion in accordance with an illustrative embodiment of the present invention;

FIG. 5 is schematic block diagram of an exemplary web based environment for measuring tension and providing draw control in accordance with an illustrative embodiment of the present invention;

FIG. 6 is a flowchart detailing the steps of a procedure for determining tension and providing draw control in accordance with an illustrative embodiment of the present invention;

FIG. 7 is a schematic block diagram of an exemplary web material production line for use in cut to length applications in accordance with an illustrative embodiment of the present invention;

FIG. 8 is a flowchart detailing the steps of a procedure for performing cut to length applications in accordance with an illustrative embodiment of the present invention; and

FIG. 9 is a flowchart detailing the steps of a procedure for obtaining statistical information using a linear sensor in accordance with an illustrative embodiment of the present invention.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT A. Overview

Illustratively, the linear sensors utilized in illustrative embodiments of the present invention are those described in the above incorporated U.S. patent applications Ser. Nos. 11/763,752, 11/763,785 and 12/100,100. However, it should be noted that the principles of the present invention may be utilized with any suitable linear sensor. As such, the description of linear sensors described in the incorporated applications should be taken as exemplary only.

Furthermore, while this description is written in terms of linear sensors that produce one-dimensional images oriented approximately parallel to the direction of motion, it will be apparent to one skilled in the art that other types of optical sensors can also be in alternative embodiments of the present invention. For example, a two-dimensional optical sensor can be used to capture two dimensional images, portions of which are then converted to one-dimensional images oriented approximately parallel to the direction of motion. The conversion can be accomplished by any suitable form of signal processing, for example by averaging light measurements approximately perpendicular to the direction of motion. As another example, a two-dimensional optical sensor capable of capturing so-called regions of interest can be used. Many commercially available CMOS optical sensors have this capability. A one-dimensional region of interest oriented approximately parallel to the direction of motion would be functionally equivalent to a linear optical sensor. The image portion or region of interest need not be the same for each captured image, but can be moved in any manner as long as the systems and methods described herein function as intended.

Illustratively, the use of one-dimensional images permits a much higher capture and analysis rate, at lower cost, than prior art systems that use two-dimensional images for detection and location. An illustrative vision detector described in pending U.S. patent application Ser. No. 10/865,155, for example, operates at 500 images per second. Illustrative linear sensors utilized for the applications described herein typically operate at over 8000 images per second, and at far lower cost. The above-referenced vision detector patent application does not describe or contemplate that one-dimensional images oriented approximately parallel to the direction of motion could be used for the purposes described herein, or that latency could be eliminated by any means.

As used herein a process refers to systematic set of actions directed to some purpose, carried out by any suitable apparatus, including but not limited to a mechanism, device, component, software, or firmware, or any combination thereof that work together in one location or a variety of locations to carry out the intended actions. A system according to the invention may include suitable processes, in addition to other elements. The description herein generally describes embodiments of systems according to the invention, wherein such systems comprise various processes and other elements. It will be understood by one of ordinary skill in the art that descriptions can easily be understood to describe methods according to the invention, where the processes and other elements that comprise the systems would correspond to steps in the methods.

B. Detection and Location of Objects

FIG. 1 is an exemplary environment for detecting and locating objects using linear sensors in accordance with an illustrative embodiment of the present invention. Conveyer 100, or other devices to induce motion, moves boxes 110, 112, 114, 116, and 118 in direction of motion 102. Each box in this example includes a label, such as example label 120, and a decorative marking, such as example marking 122. A printer 130 prints characters, such as example characters 132, on each label as it passes by. In the example of FIG. 1, the labels are the objects to be detected and located.

The illustrated linear sensor 150 provides signal 134 to printer 130 at times when labels to be printed pass, or are in some desirable position relative to, reference point 106. In an illustrative embodiment signal 134 comprises a pulse indicating that a label has been detected, and wherein the leading edge of the pulse occurs at the time that a label is at reference point 106 and thereby serves to locate the label.

Linear sensor 150 uses lens 164 to form a one-dimensional image of field of view 170 on linear optical sensor 160 comprising linear array of photoreceptors 162. Field of view 170 and linear array of photoreceptors 162 are oriented so as to produce one-dimensional images oriented approximately parallel to the direction of motion. Each photoreceptor makes a light measurement in the field of view. The exemplary linear sensor embodiment described herein with reference to FIG. 1 may be utilized to detect and track discrete objects, e.g., boxes, in a production environment. Various embodiments of such environments are described in the above-incorporated U.S. patent applications.

FIG. 2 illustrates an example application of an illustrative embodiment of the invention to track a continuous web material in accordance with an illustrative embodiment of the present invention. The web material 210, which may comprise a woven or non-woven material, e.g., paper, diapers, etc., moves in direction of motion 220 relative to apparatus 230. The web material 210 contains object features in the form of surface microstructure that gives rise to image features when illuminated by grazing illumination 250. Images are formed using telecentric lens 240 so that the optical magnification is constant in the presence of fluctuations in distance between web 210 and apparatus 230. As will be appreciated by one skilled in the art, the use of grazing illumination and telecentric optics are well-known in the art.

Apparatus 230 operates in accordance with an illustrative embodiment of the invention to output motion signal 235, which in an illustrative embodiment is a quadrature signal. With the arrangement of FIG. 2, motion signal 235 provides information about the true motion of web 210, in contrast to the indirect and, at times, inaccurate information that might be provided by a conventional mechanical encoder attached to a drive shaft of the transport mechanism. Thus, use of an exemplary linear sensor measuring technique in accordance with an illustrative embodiment of the present invention provides for more accurate measurements and enables additional functions to be performed, as described further below.

In an illustrative embodiment, linear optical sensor 240 is calibrated to compensate for any non-uniformity of illumination, optics, and response of the individual photoreceptors. A uniformly white object is placed in the field of view, or moved continuously in the field of view, and the gain for each of the three zones is set so that the brightest pixels are just below saturation. Then a calibration value is computed for each pixel, such that when each gray level is multiplied by the corresponding calibration value, a uniform image is produced for the uniformly white object. The calibration values are illustratively stored in flash memory 322 (see FIG. 3) and applied to subsequent captured images. The calibration values are limited such that each gray level is multiplied by no more than 8. Each image used by the calibration procedure is obtained by averaging 512 captured images.

Any suitable means can be employed to illuminate the field of view of linear optical sensor 340. In an illustrative embodiment, two 630 nm LEDs are aimed at the field of view from one side of linear optical sensor 340, and two 516 nm LEDs are aimed at the field of view from the other side. A light-shaping diffuser, such as those manufactured by Luminit of Torrance, Calif., is placed in front of the LEDs so that their beams are spread out parallel to linear optical sensor 340. In another illustrative embodiment, LEDs are placed to form grazing illumination suitable for imaging surface microstructure.

Human users, such as manufacturing technicians, can control the system by means of human-machine interface (HMI) 350. In an illustrative embodiment, HMI 350 comprises an arrangement of buttons and indicator lights. Processor 310 controls HMI 350 using PIO interface 332. In other embodiments, an HMI consists of a personal computer or like device; in still other embodiments, no HMI is used.

C. Apparatus

FIG. 3 is a block diagram of an illustrative embodiment of a portion of a linear detector in accordance with an illustrative embodiment of the present invention. Microcontroller 300, such as the AT91SAM7S64 sold by Atmel Corporation of San Jose, Calif., comprises ARMv4T processor 310, read/write SRAM memory 320, read-only flash memory 322, universal synchronous/asynchronous receiver transmitter (USART) 330, and a parallel I/O interface (PIO) 332. ARMv4T processor 310 controls the other elements of microcontroller 300 and executes software instructions 324 stored in either SRAM 320 or flash 322 for a variety of purposes. SRAM 320 holds data 326 used by ARMv4T processor 310. Microcontroller 300 illustratively operates at a clock frequency of 50 MHz.

Linear optical sensor 340, such as the TSL3301-LF sold by Texas Advanced Optoelectronic Solutions (TAOS) of Plano, Tex., comprises a linear array of photoreceptors. Linear optical sensor 340, under control of ARMv4T processor 310 by commands issued using USART 330, can expose the linear array of photoreceptors to light for an adjustable period of time called the exposure interval, and can digitize the resulting light measurements and transmit them in digital form to USART 330 for storage in SRAM 320. Linear optical sensor 340, also under control of ARMv4T processor 310, can apply an adjustable analog gain and offset to the light measurements of each of three zones before being digitized, as described in TAOS document TAOS0078, January 2006.

The linear sensor illustrated in FIG. 3 produces signal 362 for purposes including indicating detection and location of objects. Signal 362 is connected to automation equipment 360 as required by a given application. Note that automation equipment 360 is shown for illustrative purposes only; signal 362 may be used for any purpose and need not be connected to any form of automation equipment, and signal 362 need not be used at all.

In an illustrative embodiment, various processes are carried out by an interacting collection of digital hardware elements, including those shown in the block diagram of FIG. 3, suitable software instructions residing in SRAM 320 or flash 322, and data residing in SRAM 320. In the illustrative apparatus of FIG. 3, a capture procedure comprises digitizing the light measurements so as to obtain an array of numbers, called pixels, whose values, called gray levels, correspond to the light measurements; transferring the pixels from linear optical sensor 340 to microcontroller 300; and storing the pixels into SRAM memory 320 for subsequent analysis. Following the usual convention in the art, a pixel may refer either to an element of the array of numbers, or to a unit of distance corresponding to the distance between two adjacent elements of the array. The array of pixels is a one-dimensional digital image.

It will be apparent to one skilled in the art that “approximately parallel” refers to any orientation that allows the linear detector to obtain a time-sequence of images of a slice of an object in a plurality of positions as it enters, moves within, and/or exits the field of view. It will further be apparent that the range of orientations suitable for use for with the systems and methods described herein has a limit that depends on a particular application of the invention. For example, if the orientation of the image is such that the angle between the image orientation and the direction of motion is 5 degrees, the object will drift 0.09 pixels perpendicular to the direction of motion for every pixel it moves parallel to that direction. If the range of the plurality of positions covers 30 pixels in the direction of motion, for example, the drift will be only 2.6 pixels. If the systems and methods described herein function as intended with a 2.6 pixel drift in a given application of the invention, the example 5 degree orientation would be approximately parallel for that application.

Similarly, it will be apparent to one skilled in the art that the direction of motion need not be exactly uniform or consistent, as long as the systems and methods described herein function as intended. The use of one-dimensional images allows very high capture and analysis rates at very low cost compared to prior art two-dimensional systems. The high capture and analysis rate allows many images of each object to be analyzed as it passes through the field of view. The object motion ensures that the image are obtained from a plurality viewing perspectives, giving far more information about the object than can be obtained from a single perspective. This information provides a basis for reliable detection and accurate location.

FIG. 4 shows a portion of an illustrative capture process that obtains one dimensional image 430 of field of view 410, where image 430 is oriented approximately parallel to direction of motion 400. Light emitted from field of view 410 is focused onto an optical sensor (not shown), which makes light measurements. In the illustrative capture process of FIG. 4, 24 discrete light measurements are made in 24 zones of field of view 410, such as example zone 440. The zones are shown as rectangular, contiguous, and non-overlapping for ease of illustration, but for typical sensors the geometry is more complex, due in part to the nature of the optics used to focus the light and the requirements of semiconductor fabrication. In the illustrative capture process of FIG. 4, each light measurement is digitized to produce 24 pixels, such as example pixel 450, which corresponds to example zone 440. The gray level of example pixel 450 is 56, which is the light measurement for example zone 440. The zones of FIG. 4 may correspond, for example, to individual photoreceptors in a linear array sensor, or to a plurality of photo receptors of a two-dimensional sensor that have been converted to a single measurement by any suitable form of signal processing, as described above.

The geometry of the light measurement zones of field of view 410 define image orientation 420 of image 430. Image 430 is oriented approximately parallel to direction of motion 400 if image orientation 420 and direction of motion 400 are such that the capture process can obtain a time-sequence of images of a slice of an object in a plurality of positions as it enters, moves within, and/or exits the field of view. Note that image orientation 420 is a direction relative to field of view 410, as defined by the geometry of light measurements contained in image 430. The image itself is just an array of numbers residing in a digital memory; there is no significance to its horizontal orientation in FIG. 4.

As used herein a measurement process makes measurements in the field of view by analyzing captured images and producing values called image measurements. Example image measurements include brightness, contrast, edge quality, edge position, number of edges, peak correlation value, and peak correlation position. Many other image measurements are known in the art that can be used within the scope of the invention. Image measurements may be obtained by any suitable form of analog and/or digital signal processing.

In the illustrative embodiment of FIG. 3, a measurement process comprises a digital computation carried out by ARMv4T processor 310, operating on a captured image stored in SRAM 320, under the control of software instructions stored in either SRAM 320 or flash 322. For example, a brightness image measurement may be made by computing the average of the pixels of an image or portion thereof; a contrast image measurement may be made by computing the standard deviation of the pixels of an image or portion thereof.

In the illustrative embodiment of FIG. 3, a selection process comprises a digital computation carried out by ARMv4T processor 310, operating on image measurements stored in SRAM 320 or in the registers of ARMv4T processor 310, under the control of software instructions stored in either SRAM 320 or flash 322.

A linear sensor according to the invention may include a decision process whose purpose is to analyze object measurements so as to produce object information. In the illustrative embodiment of FIG. 3, a decision process comprises a digital computation carried out by ARMv4T processor 310, operating on object measurements stored in SRAM 320 or in the registers of ARMv4T processor 310, under the control of software instructions stored in either SRAM 320 or flash 322.

A linear sensor according to some embodiments of the invention may optionally include a signaling process whose purpose is to produce a signal that communicates object information. A signal can take any form known in the art, including but not limited to an electrical pulse, an analog voltage or current, data transmitted on a serial, USB, or Ethernet line, radio or light transmission, and messages sent or function calls to software routines. The signal may be produced autonomously by the linear sensor, or may be produced in response to a request from other equipment.

In the illustrative embodiment of FIG. 3, a signaling process comprises a digital computation carried out by ARMv4T processor 310, operating on object information stored in SRAM 320 or in the registers of ARMv4T processor 310, producing signal 362, and under the control of software instructions stored in either SRAM 320 or flash 322. Signal 362 is an electrical pulse, which the ARMv4T processor 310 illustratively ensures that the pulse appears at a precise time.

D. Tension Measurement and Draw Control Applications

One illustrative application for linear sensors is maintaining draw control of a web material in a production environment. Illustratively, web materials are maintained with a set tension (or a predefined range of acceptable tensions) along the length of the material as the material traverses the production environment. At various points along the material, servo motors work to induce movement into the web material. Appropriate tension needs be maintained along the web material to prevent sagging and/or prevent the material from tearing due to excess tension. By utilizing a linear sensor in accordance with an illustrative embodiment of the present invention, tension and draw control may be maintained without requiring physical contact with the web based material.

FIG. 5 is a schematic block diagram of an exemplary web-based material production line environment 500 in accordance with an illustrative embodiment of the present invention. A web material 505, e.g., paper, cloth, paper towel material, etc., is transported in a direction of motion 510 by one or more servo motors 515. As will be appreciated by one skilled in the art, the motors 515 may be spaced along the web material based on a variety of factors, e.g., type of material, distance traveled, etc.

Illustratively, two linear sensors 525A, B are configured to measure the velocity of the material 505 at a first point 530A and a second point 530B respectively along the web material. The linear sensors are illustratively one dimensional linear sensors that are arranged approximately parallel to the direction of motion 510 of the web material 505. The linear sensors 525A,B may measure velocity using any technique for velocity measurement using linear sensors. Illustratively, the linear sensors utilize the technique described in the above-incorporated U.S. patent application. However, it should be noted that in alternative embodiments, any technique for measuring velocity may be utilized. As such, the description of linear sensors arranged parallel to the direction of motion of the web material should be taken as exemplary only.

The linear sensors 525A,B and the servo motor 515 are operatively interconnected with a control unit 520. The control unit 520 receives the velocity measurements from the linear sensors and determines the acceleration of the web material 505 between the first point 530A and the second point 530B by, e.g., determining the difference between the two velocities. As acceleration is proportional to force, the tension along the web material is proportional to the acceleration of the web material. The control unit 520 is further configured to output appropriate control signals to the servo motor 515 to (de)accelerate and thereby modify the tension along the web material.

It should be noted that while the environment 500 is shown with a single pair of linear sensors operatively connected to a single control unit managing one servo motor, the principles of the present invention may be utilized in more complex environments. For example, a factory wide control unit may manage a plurality of pairs of linear sensors, a plurality of servo motors, etc. Such a factory management system may utilize wireless communication systems enabling the various components to communicate over the production line without requiring physical cabling interconnecting them. As such, the description of environment 500 should be taken as exemplary only.

FIG. 6 is a flowchart detailing the steps of a procedure 600 for determining tension and controlling draw in accordance with an illustrative embodiment of the present invention. The procedure 600 begins in step 605 and continues to step 610 where velocity measurements are obtained at a first point and a second point along a web material. Illustratively, the first and second points are associated with a first and second linear sensors, shown above in reference to environment 500 of FIG. 5. The acceleration between the first and second points is then determined in step 615. Illustratively, acceleration may be determined by examining the difference between the velocities at the first and second points. Assuming that the web material is moving in a substantially straight line, the difference in speed between the first and second point in conjunction with a known distance between two points provides the information necessary to determine the acceleration of the web material. The acceleration of the web material is proportional to the force applied by the servo motor 515.

Depending on the amount of force being applied to the web material, the control unit may output appropriate control signals to the servo of the motor 515 to maintain satisfactory tension on the web material 505 in step 620. That is, the control unit may output control signals to maintain the tension within a predefined range of tensions. As will be appreciated by one skilled in the art, the predefined ranges will vary with the type of material that is utilized. Illustratively, should insufficient force be applied to the web material, the control signals may signify that the servo motor should accelerate to induce additional tension. Similarly, should a determination be made that insufficient or too much attention is being applied, the control signals may cause the servo motor to slow down toward the accelerate, thereby reducing the tension on the web material. The procedure 600 then completes in step 625.

E. Cut to Length Applications

Another illustrative application for linear sensors may comprise cut to length applications. Cut to length applications are those applications where a certain operation is performed after a variable and/or predefined distance of webbing material has passed a given point. For example, if the webbing material comprises paper towel material, perforations may need to be made at substantially regular intervals. Similarly, if the webbing material comprises a child's diaper material, the material may need to be cut at regular intervals. More generally, cut to length applications are those applications that require some operation to be performed at substantially regular intervals along the length of the web material. The operations may comprise, for example, cutting the material, marking the material, forming perforations on the material, printing something on the material, except. As such, the operations described herein should be taken as exemplary only. One skilled in the art will appreciate that any operations may be utilized at substantially regular intervals along a web material.

FIG. 7 is a schematic block diagram of an exemplary cut to length application environment 700 in accordance with an illustrative embodiment of the present invention. The web material 505 moves along direction of motion 510, similar to environment 500 described above in respect to FIG. 5. A linear sensor 525 is illustratively arranged parallel to the direction of motion 510 of the material 505. An actuator 710is configured to perform an action a point 705 along the web 505. Illustratively, the actuator 710 may cut the web material 505 at point 710. However, in alternative embodiments, the actuator may perforate the material, print on the material, etc. As such, the description of the material being cut should be taken as exemplary only. In the illustrative environment 700, the material 505 has been perforated at locations 715A,B at a predefined interval.

A control unit 520 is operatively interconnected with the linear sensor 525 and the actuator 710. The control unit 520 is illustratively configured to receive distance measurements from the linear sensor 525 as to the distance that the web material 505 has traveled. Illustratively, these signals output from the linear sensor 525 may be in a quadrature format, such as those typically output from conventional shaft encoders. However, in alternative embodiments of the present invention differing formats may be utilized. As such, the description of quadrature outputs to be taken as exemplary only. It should be noted that by configuring a linear sensor 525 to output distance measurements, a linear sensor 525 may replace a conventional shaft encoder. Thus, the linear sensor may be utilized in conventional servo control systems in place of a shaft encoder unit. In accordance with an illustrative embodiment of the present invention, the control unit 520 detects that the web material 505 has moved a certain length. In response, the control unit generates a trigger signal to the actuator 710. The actuator then performs an action on the web material 505. Illustratively, the trigger signal is timed so that the actuator performs the desired action on the Web material at a predefined distance from a previous point along the material.

FIG. 8 is a flowchart detailing the steps of a procedure 800 for performing cut to length applications in accordance with an illustrative embodiment of the present invention. The procedure 800 begins in step 805 and continues to step 810 where a quantity (length) of web material is measured as having moved past a selected point. Illustratively, a linear sensor is utilized to measure the web material as it moves past a selected point. The control unit generates a trigger signal based on the distance of material traveled in step 815. Illustratively, the trigger signal is generated so that the delay from the generation of the trigger signal is such that the material has moved the proper distance before the action is performed on the material. For example, if the material is moving at 10 m/s and the trigger delay (i.e., the time between generation of the trigger signal and the occurrence of the action) is 0.1 s, then the trigger signal needs to occur after the material has moved 1 m less than the desired distance. The material will then move the final 1 m in the time it takes for the trigger signal to activate the action to be performed.

An actuator receives the generated trigger signal and performs an action in step 820. The action may comprise any actuator operation, including, e.g., cutting the web material, perforating the web material, printing onto the web material, etc. By utilizing linear sensor is, conventional shaft encoders and/or other physical means of a measurement distance traveled may be replaced. The procedure 800 then completes in step 825.

F. Statistical Data Acquisition Applications

Another application that may utilize linear sensors is the acquisition of statistical data regarding materials and/or objects in a production environment. Such statistical data may be utilized in a factory management system to ensure quality control of the materials and/or objects being produced. Furthermore, the statistical data may also be utilized by technicians for identification of error conditions within a production line, or may be utilized to fine tune a production line increase output, thereby resulting in additional units produced.

FIG. 9 is a flowchart detailing the steps of a procedure 900 for acquiring statistical data in accordance with an illustrative embodiment of the present invention. The procedure 900 begins in step 905 and continues to step 910 where the material moves along a conveyor. As material moves along the conveyor, a linear sensor scans the material. The linear sensor may be utilized in any of the other applications described herein or in applications not described herein. That is, the linear sensors may be utilized solely for statistical data acquisition or may be utilized for, e.g., cut to length applications, etc. However, in conjunction with the acquisition for be functioning of any other application, the linear detector acquires statistical data from one or more points along the material in step 915. Such statistical data may comprise, e.g., average tension along the material, average speed of the material, etc. In alternative embodiments, the statistical data may comprise image-based characteristics of the web material being inspected, e.g., a histogram of texture of the web material versus time, maximum/minimum responses to determine defects, etc. For those web materials that should have repetitive patterns, the regularity of the appearance of those patterns may be utilized as statistical data that may be used in determining a quality score.

The system then calculate statistics and a quality score in step 925. The quality score may be calculated using a variety of formulas. Illustratively, the quality score may be determined based on whether a brightness peak is greater than/less than a threshold. In an illustrative embodiment of the present invention, the threshold may be predefined; however, in alternative embodiments, the threshold may be variable. For those web materials that should have a substantially constant texture, a quality score may be calculated by determining the location of the peak of a histogram of the material texture is between a low texture value (TL) and a high texture value (TH). Similarly, for those web materials that have a distance repetitive texture, the quality value may be calculated by determining the peak histogram of the material and comparing it to a TL/TH values that vary along the distance of the web material.

In an illustrative embodiment of the present invention, the procedure determines what the material meets a minimum quality score in step 930. If so, the material is accepted in step 935 and the procedure completes in step 940. However, if in step 930 the material does not meet a minimum quality score, the procedure branches to step 945 where the material is rejected. This may occur when, e.g., a splice occurs during manufacturing. A splice occurs when an end of a first roll of web material is spliced onto the end of a second roll of the material. Manufacturers typically do not desire to utilize the region where the splice occurs. By computing appropriate quality scores, the splice regions may be detected and rejected, thereby preventing the splice regions from being utilized in a manufactured product. The procedure then completes in step 940.

As will be appreciated by one skilled in the art, the principles of the present invention may be utilized in a variety of production environments. As such, the various specific examples and embodiments described herein should be taken as exemplary. It is expressly contemplated that the applications of linear sensors described herein may be centrally managed by a factory management system. Furthermore, while the applications of linear sensors described herein have utilized one dimensional linear sensors arranged approximately parallel to a direction of motion, the principles of the present invention may be utilized with additional and/or differing linear sensors including, for example, those arranged perpendicular to a direction of travel, multi-dimensional sensors, etc. As such, descriptions contained herein should be taken as exemplary only.

The foregoing has been a detailed description of various embodiments of the invention. It is expressly contemplated that a wide range of modifications, omissions, and additions in form and detail can be made hereto without departing from the spirit and scope of this invention. For example, the processors and computing devices herein are exemplary and a variety of processors and computers, both standalone and distributed can be employed to perform computations herein. Likewise, the linear array sensor described herein is exemplary and improved or differing components can be employed within the teachings of this invention. Numerical constants used herein pertain to illustrative embodiments; any other suitable values or methods for carrying out the desired operations can be used within the scope of the invention. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention. 

1. A method for draw control of a web material, the method comprising: obtaining, using a first linear sensor, a first velocity measurement at a first point along the web material; obtaining, using a second linear sensor, a second velocity measurement at a second point along the web material; determining, using the first and second velocity measurements, an acceleration of the web material between the first and second points; and adjusting tension on the web material based on the determined acceleration.
 2. The method of claim 1 wherein the web material comprises a woven material.
 3. The method of claim 1 wherein the web material comprises a non-woven material.
 4. The method of claim 1 wherein the first linear sensor comprises a one dimensional sensor arranged approximately parallel to a direction of motion of the web material.
 5. The method of claim 1 wherein the second linear sensor comprises a one dimensional sensor arranged approximately parallel to a direction of motion of the web material.
 6. The method of claim 1 wherein adjusting tension on the web material based on the determined acceleration comprises modifying a speed of a motor configured to move the web material.
 7. The method of claim 1 wherein the first linear sensor is located prior to a motor controlling speed of the web material and wherein the second linear sensor is located after the motor.
 8. The method of claim 1 wherein adjusting tension on the web material based on the determined acceleration comprises sending a control signal to a motor.
 9. A system for draw control of a web material, the system comprising: a motor configured to provide motion to the web material; a first linear sensor configured to obtain a first velocity at a first point along the web material; a second linear sensor configured to obtain a second velocity at a second point along the web material; a control unit configured to determine an acceleration of the web material between the first and second points using the first and second velocities and further configured to transmit a control signal to the motor to cause a change in acceleration of the web material thereby maintaining a tension along the web material within a predefined range.
 10. The system of claim 9 wherein the web material comprises a woven material.
 11. The system of claim 9 wherein the web material comprises non-woven material.
 12. The system of claim 9 wherein the first linear sensor comprises a one dimensional sensor arranged approximately parallel to a direction of motion of the web material.
 13. The system of claim 9 wherein the second linear sensor comprises a one dimensional sensor arranged approximately parallel to a direction of motion of the web material.
 14. A method for performing cut to length operation on a web material, the method comprising: determining, using a linear sensor, a length of the web material that has passed a predefined point; generating a trigger signal to activate an actuator to perform an action on the web material; and performing, by the actuator, the action on the web material, wherein the trigger signal is timed so that the action is performed on the web material at predefined distances along the web material.
 15. The method of claim 14 wherein the generation of the trigger signal is performed by a control unit.
 16. The method of claim 14 wherein the generation of the trigger signal is performed by the linear sensor.
 17. The method of claim 14 wherein the predefined distance comprises substantially equal distances.
 18. The method of claim 14 wherein the predefined distance comprises a set of variable distances.
 19. The method of claim 14 wherein the action comprises cutting the web material.
 20. The method of claim 14 wherein the action comprises printing on the web material.
 21. A system for performing cut to length operation on a web material, the system comprising: a linear sensor configured to determine a length of the web material passing a predefined point; a control unit operative interconnected with the linear sensor, the control unit configured to generate a trigger signal; an actuator, responsive to the trigger signal, configured to perform an action on the web material wherein the trigger signal is timed so that the action is performed on the web material at a predefined location on the web material.
 22. A method for ensuring quality control of a web material, the method comprising: obtaining a data set of statistical data from one or more points along the web material using one or more linear a sensors; and calculating a quality score using the set of statistics.
 23. The method of claim 22 wherein the statistical data comprises image-based data o the web material.
 24. The method of claim 22 further comprising determining whether the calculated quality score meets a predefined minimum quality score; and in response to determining that the quality score does not meet the predefined minimum quality score, rejecting at least a portion of the web material.
 25. The method of claim 22 wherein the set of statistical data comprises an average speed of the web material.
 26. The method of claim 22 wherein the set of statistical data comprises a set of changes in tension along the web material. 